Multi-layer dielectric containing diffusion barrier material

ABSTRACT

A method for forming a dielectric is disclosed. The method comprises forming a first dielectric layer over semiconductor material. A diffusion barrier material is introduced into the first dielectric layer. Lastly, a second dielectric layer is formed over the first dielectric layer after the introducing.

BACKGROUND

The present disclosures relate to semiconductor devices andsemiconductor device manufacturing, and more particularly, to amulti-layer dielectric containing diffusion barrier material.

RELATED ART

As the dimensions of semiconductor devices continue to get smaller andsmaller, various semiconductor device design requirements must be met.For example, the design requirements for a silicon nitride gatedielectric may include one or more of reducing gate leakage, maintainingor improving device performance (Gm, mobility) with a targeted thresholdvoltage. In addition, the design requirements may require a reducednegative bias temperature instability (NBTI), where V_(T) shift afterhigh temp stressing is a big problem on silicon nitride (SiN) or siliconoxynitride (SiON).

One possible way to reduce gate leakage includes using silicon nitride(SiN) on a single crystal substrate. The dielectric constant (k) of pureSiN is on the order of approximately 7.8. Accordingly, the dielectricconstant (k) of pure SiN is approximately two times (twice) that ofSiO₂. However, one problem with using pure deposited SiN is that itproduces a high interface state density (Dit) and bulk traps.

Accordingly, there is needed a structure and method for overcoming theproblems in the art as outlined above.

SUMMARY

According to one embodiment, a method for forming a dielectric comprisesforming a first dielectric layer over semiconductor material;introducing a diffusion barrier material into the first dielectriclayer; and forming a second dielectric layer over the first dielectriclayer after the introducing.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the present disclosure are illustrated by way ofexample and not limited by the accompanying figures, in which likereferences indicate similar elements, and in which:

FIG. 1 is a cross-sectional view of a portion of a multi-layerdielectric structure during fabrication according to one embodiment ofthe present disclosure;

FIG. 2 is a cross-sectional view of the portion of the multi-layerdielectric structure of FIG. 1 during further fabrication according toone embodiment of the present disclosure;

FIG. 3 is a graphical representation of a nitrogen concentration profilewithin the portion of the multi-layer dielectric structure of FIG. 2;and

FIG. 4 is a cross-sectional view of the multi-layer dielectric structureaccording to an embodiment of the present disclosure.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help improve anunderstanding of the embodiments of the present disclosure.

DETAILED DESCRIPTION

As will be discussed further herein, the present embodiments provide alow nitrogen concentration at a lower interface between the firstdielectric layer and the substrate, to minimize interface state density(Dit) and minimize fixed charges (or bulk traps). One such interfaceincludes a SiON/Si interface. The present embodiments further provide alow nitrogen concentration at the lower interface, between the firstdielectric layer and the substrate, to reduce negative bias temperatureinstability.

In addition, the embodiments of the present disclosure provide highnitrogen concentration in at least an interface between the firstdielectric layer and the second dielectric layer to block undesireddopant penetration. For example, the interface may include an interfacebetween a high K (or medium K) dielectric and an underlying SiON,wherein the high nitrogen concentration acts as a barrier layer to blockundesired dopant penetration from an overlying P+ poly gate or metalgate.

FIG. 1 is a cross-sectional view of a portion of a multi-layerdielectric structure during fabrication according to one embodiment ofthe present disclosure. A wafer structure 10 includes a substrate 12having a dielectric layer 14 disposed thereon, forming an interface 16between the substrate and the dielectric layer. Substrate 12 may includeany one of a bulk silicon substrate, an SOI substrate, or other singlecrystal substrate. In one embodiment, the dielectric layer 14 includes asilicon dioxide (SiO₂) layer. Silicon dioxide layer 14 is formed onsubstrate 12, using any well known technique, to have a thickness on theorder of approximately 10 to 15 angstroms or less. Furthermore, layer 14has a top surface 18.

Subsequent to forming layer 14, the wafer structure 10 is processed in amanner to transform layer 14 into a nitrided oxide layer. In oneembodiment, layer 14 is transformed into a plasma nitrided oxide layer(PNO layer). Forming the PNO includes exposing layer 14 to a plasmanitridation process 20. The plasma nitridation process 20 includes usinga pure nitrogen gas 20 a fed into plasma 20 b for creation of ionic andradical species of N⁺ and N₂* (denoted by reference numeral 20 c)impinging upon surface 18 of layer 14. Furthermore, the plasma nitridedthin base oxide layer incorporates a small amount of N at the bottominterface and a relatively high N at the top interface. Plasma sourcesare known in the art and not further discussed herein. In anotherembodiment, layer 14 can be transformed into the nitrided oxide layerusing nitrogen implantation, a thermal anneal using a nitrogen species,or other suitable method.

FIG. 2 is a cross-sectional view of the portion of the multi-layerdielectric structure of FIG. 1 during further fabrication according toone embodiment of the present disclosure. That is, a second dielectriclayer 22 is formed on surface 18 of layer 14, the second dielectriclayer 22 having a thickness on the order of approximately 10–30angstroms or more, depending upon the material of the layer. Seconddielectric layer 22 includes a high k or medium k dielectric material,to include at least one of metal oxide, metal silicate, or metaloxynitride. A top surface of dielectric layer 22 is denoted by referencenumeral 24. The dielectric material can include one or more othermaterials as provided herein below.

In one embodiment, dielectric layer 22 includes silicon nitride (Si₃N₄)for providing a high level of nitrogen at the top of dielectric layer14. Depositing silicon nitride on top of the PNO layer 14 takesadvantage of the gradual gradient N profile of the PNO layer. Lastly,one or more of the following may be used for the Si₃N₄ depositionincluding: atomic layer deposition (ALD) SiN deposition, rapid thermalchemical vapor deposition (RTCVD), low pressure chemical vapordeposition (LPCVD) SiN, or plasma enhanced CVD (PECVD) SiN to achieve afinal nitrogen profile close to an ideal profile.

Formation of the second dielectric layer 22 upon layer 14 also includesthe forming of a diffusion barrier, wherein the diffusion barrier isformed at least at the surface 18 of layer 14. In one embodiment, thediffusion barrier includes a thin layer of nitrogen having a thicknesson the order of less than 10 angstroms. The diffusion barrier preventspenetration of undesired dopants from subsequently formed layers, suchas, a subsequently formed gate electrode. In another embodiment, thesecond dielectric layer forms a diffusion. barrier that includes theentire second dielectric layer, for example, a pure nitride layer.

FIG. 3 is a graphical representation of a nitrogen concentration profilewithin the portion of the multi-layer dielectric structure of FIG. 2. Inparticular, the graphical representation profile is shown in terms ofnitrogen concentration across the depths of layers 22, 14, and 12. Thevertical axis includes nitrogen concentration in units of number ofnitrogen atoms per cubic centimeter (#/cm³). The horizontal axisincludes a depth dimension representation of layers 22, 14, and 12, aswell as respective surfaces/interfaces 24, 18, and 16.

In one example, as shown, dielectric layer 22 contains a nitrogenconcentration profile on the order of approximately 4×10²¹ per cm³throughout the depth dimension of layer 22, that is, across the depth oflayer 22 from surface 24 to surface 18 of layer 14. Layer 14 includes anitrogen concentration profile in the form of a gradual gradient,beginning with a nitrogen concentration on the order of approximately4×10²¹ per cm³ at surface/interface 18 and gradually decreasing to alevel on the order of approximately 2×10²⁰ per cm³ at surface/interface16 of substrate 12. The nitrogen concentration proximatesurface/interface 16 preferably includes a minimal nitrogenincorporation. In addition, from the surface/interface 16, the nitrogenconcentration further diminishes with depth within substrate 12.

In addition, other nitrogen concentration profiles for layer 22 arepossible. For example, layer 22 may not contain any nitrogen at all.Moreover, layer 22 may contain a different profile and/or level ofnitrogen than as shown in FIG. 3.

FIG. 4 is a cross-sectional view of the multi-layer dielectric structureaccording to an embodiment of the present disclosure. In particular, agate electrode 26 is formed on surface 24 of dielectric layer 22. Gateelectrode 26 includes either one of a poly material or a metal, having athickness sufficient for an intended semiconductor device. Forming thegate electrode 26 includes forming a layer of gate material over thesecond dielectric layer and patterning the layer of gate material toform a gate from the layer of gate material, the gate being located overthe second dielectric layer.

The stack structure of the present embodiments include a gradient Nconcentration profile within the first dielectric layer 14, with a lowconcentration of N at the bottom interface between the first dielectriclayer and the underlying substrate. The stack structure further includesa total high overall N concentration that provides an overall higherdielectric constant (k) and lower leakage current (Jg).

Accordingly, the present embodiments advantageously provide for overallhigher k, better carrier mobility, smaller VT shift and small NBTI dueto lower N amount at the SiO₂/Si interface. The embodiments also reduceand/or prevent undesired boron (B) penetration due to most of nitrogenbeing distributed at the top of the SiON, resulting in better dielectricreliability (TDDB) and reduced Vt shift. The embodiments still furtherprovide lower Dit, and further provide for higher performance and hotcarrier immunity (HCI). The higher performance and HCI are provided dueto low N concentration at the bottom interface, between the firstdielectric layer 14 and the underlying substrate 12. Still further, theembodiments provide benefits of T_(ox) scalability and gate leakagereduction due to high nitrogen at the bulk of the gate dielectric.

According to one embodiment, the multi-layer dielectric structureincludes a two-step nitridation process. The two-step nitridationprocess utilizes different controllable nitridation conditions of eachstep to achieve a high [N] at the top interface and the bulk, as well aslow [N] at the bottom interface.

According to one embodiment of the present disclosure, a method forforming a dielectric includes forming a first dielectric layer oversemiconductor material, introducing a diffusion barrier material intothe first dielectric layer, and forming a second dielectric layer overthe first dielectric layer after the introducing.

In one embodiment, the diffusion layer material includes nitrogen andthe second dielectric layer is a relatively higher K dielectric than thefirst dielectric layer. The process of introducing a diffusion barriermaterial into the first dielectric layer includes at least one of thefollowing: performing plasma processing of the diffusion barriermaterial into the first dielectric layer; implanting the diffusionbarrier material into the first dielectric layer; and performing athermal anneal of material including the diffusion barrier material intothe first dielectric layer.

In one embodiment, the semiconductor material includes silicon. Thesemiconductor material includes at least one of single crystal silicon,strained silicon, or silicon germanium. In another embodiment, the firstdielectric layer includes silicon dioxide. Alternatively, the firstdielectric layer can include at least one of germanium oxide and silicongermanium oxide. In yet another embodiment, the second dielectric layerincludes silicon nitride. Alternatively, the second dielectric layerincludes at least one of germanium nitride, silicon germanium nitride,and a metal silicon oxynitride.

Still further, the second dielectric layer can include a high Kdielectric, wherein the high K dielectric includes at least one of ametal oxide, a metal silicate, and a metal oxynitride. The metal oxideincludes at least one of hafnium oxide, aluminum oxide, lanthanum oxide,titanium oxide, and tantalum oxide. The metal silicate includes at leaston of hafnium silicate, aluminum silicate, lanthanum silicate, titaniumsilicate, and tantalum silicate. The metal oxynitride includes at leastone of hafnium oxynitride, aluminum oxynitride, lanthanum oxynitride,titanium oxynitride, and tantalum oxynitride. Lastly, the metal siliconoxynitride includes at least one of hafnium silicon oxynitride, aluminumsilicon oxynitride, lanthanum silicon oxynitride, titanium siliconoxynitride, and tantalum silicon oxynitride.

After the introducing, the diffusion material has a gradual gradientprofile in the first dielectric layer. In other words, after theintroducing, a bottom portion of the first dielectric layer has lowerconcentration of the diffusion barrier material than an upper portion ofthe first dielectric layer, wherein a concentration gradient profile isformed that gradually transitions from the higher concentration at theupper portion to the lower concentration at the bottom portion. Stillfurther, the introducing forms a barrier layer including the diffusionbarrier material in an upper portion of the first dielectric layer.

According to another embodiment, a method includes forming a firstdielectric layer of silicon dioxide over semiconductor material ofsilicon. Nitrogen is introduced into the first dielectric layer. Asecond dielectric layer is formed over the first dielectric layer afterthe introducing, wherein the second layer includes silicon nitride.Lastly, a layer of gate material is formed over the second dielectriclayer.

In one embodiment, the introducing includes performing a plasmanitridation process. The plasma nitridation process is characterized asa remote plasma nitridation process. In another embodiment, theintroducing includes implanting nitrogen into the first dielectriclayer. The introducing further includes annealing the first dielectriclayer after the implanting. Still further, in another embodiment, theintroducing includes flowing a nitrogen bearing gas over the firstdielectric layer and then annealing the first dielectric layer.

After the introducing, the nitrogen has a gradual gradient profile inthe first dielectric layer. In other words, after the introducing, abottom portion of the first dielectric layer has lower concentration ofnitrogen than an upper portion of the first dielectric layer.Furthermore, the introducing forms a barrier layer of silicon nitride inan upper portion of the first dielectric layer. The method furtherincludes patterning the layer of gate material to form a gate from thelayer of gate material, the gate being located over the seconddielectric layer.

According to yet another embodiment of the present disclosure, asemiconductor device includes semiconductor material; a first dielectriclayer located over the semiconductor material, wherein the firstdielectric layer includes a diffusion barrier material having a gradualgradient profile and having a higher concentration is an upper portionof the first dielectric layer and a low concentration in a lower portionof the first dielectric layer; a second deictic layer located over thefirst dielectric layer; and a gate located over the second dielectriclayer.

The diffusion layer material of the device includes nitrogen. The seconddielectric layer is a relatively higher K dielectric than the firstdielectric layer. The semiconductor material includes silicon.Alternatively, the semiconductor material can include at least one ofsingle crystal silicon, strained silicon, or silicon germanium. Inaddition, the first dielectric layer can include silicon dioxide.Alternatively, the first dielectric layer can include at least one ofgermanium oxide and silicon germanium oxide. The second dielectric layerincludes silicon nitride. Alternatively, the second dielectric layer caninclude at least one of one of germanium nitride and silicon germaniumnitride.

In another embodiment, the second dielectric layer includes a high Kdielectric. The high K dielectric includes at least one of a metaloxide, a metal silicate, and a metal oxynitride. The metal oxideincludes at least one of hafnium oxide, aluminum oxide, lanthanum oxide,titanium oxide, and tantalum oxide. The metal silicate includes at leastone of hafnium silicate, aluminum silicate, lanthanum silicate, titaniumsilicate, and tantalum silicate. The metal oxynitride includes at leastone of hafnium oxynitride, aluminum oxynitride, lanthanum oxynitride,titanium oxynitride, and tantalum oxynitride. The metal siliconoxynitride includes at least one of hafnium silicon oxynitride, aluminumsilicon oxynitride, lanthanum silicon oxynitride, titanium siliconoxynitride, and tantalum silicon oxynitride. Furthermore, the deviceincludes a barrier layer located in an upper portion of the firstdielectric layer, the barrier layer including the diffusion barriermaterial.

In the foregoing specification, the disclosure has been described withreference to various embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the present embodiments as set forthin the claims below. Accordingly, the specification and figures are tobe regarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope of thepresent embodiments.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the term“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements by may include other elements not expressly listedor inherent to such process, method, article, or apparatus.

1. A method for forming a dielectric comprising: forming a firstdielectric layer over semiconductor material; introducing a diffusionbarrier material into the first dielectric layer after the firstdielectric layer alone is formed, wherein introducing the diffusionbarrier material includes creating a gradual gradient diffusion barrierconcentration profile within the first dielectric layer in which aconcentration of the diffusion barrier material proximate a firstsurface of the first dielectric layer is an order of magnitude higherthan a concentration of the diffusion barrier material proximate asecond surface opposite the first surface, the second surface beinglocated at an interface between the first dielectric layer and thesemiconductor material; and forming a second dielectric layer over thefirst dielectric layer after the introducing.
 2. The method of claim 1wherein the diffusion layer material includes nitrogen.
 3. The method ofclaim 1 wherein the second dielectric layer is a relatively higher Kdielectric than the first dielectric layer.
 4. The method of claim 1wherein the introducing further includes: performing plasma processingof the diffusion barrier material into the first dielectric layer. 5.The method of claim 1 wherein the introducing further includes:implanting the diffusion barrier material into the first dielectriclayer.
 6. The method of claim 1 wherein the introducing furtherincludes: performing a thermal anneal of material including thediffusion barrier material into the first dielectric layer.
 7. Themethod of claim 1 wherein the semiconductor material includes silicon.8. The method of claim 7 wherein the semiconductor material includes atleast one of single crystal silicon, strained silicon, or silicongermanium.
 9. The method of claim 1 wherein the first dielectric layerincludes silicon oxide.
 10. A method for forming a dielectriccomprising: forming a first dielectric layer over semiconductormaterial; introducing a diffusion barrier material into the firstdielectric layer; and forming a second dielectric layer over the firstdielectric layer after the introducing, wherein the first dielectriclayer includes at least one of germanium oxide and silicon germaniumoxide.
 11. The method of claim 1 wherein the second dielectric layerincludes silicon nitride.
 12. A method for forming a dielectriccomprising: forming a first dielectric layer over semiconductormaterial; introducing a diffusion barrier material into the firstdielectric layer; and forming a second dielectric layer over the firstdielectric layer after the introducing, wherein the second dielectriclayer includes at least one of one of germanium nitride and silicongermanium nitride.
 13. The method of claim 1 wherein the seconddielectric layer includes a high K dielectric.
 14. The method of claim 1wherein the high K dielectric includes at least one of a metal oxide, ametal silicate, a metal oxynitride, and a metal silicon oxynitride. 15.The method of claim 14 wherein: the metal oxide includes at least one ofhafnium oxide, aluminum oxide, lanthanum oxide, titanium oxide, andtantalum oxide; the metal silicate includes at least one of hafniumsilicate, aluminum silicate, lanthanum silicate, titanium silicate, andtantalum silicate; the metal oxynitride includes at least one of hafniumoxynitride, aluminum oxynitride, lanthanum oxynitride, titaniumoxynitride, and LanLalum oxynitride; and the metal silicon oxynitrideincludes at least one of hafnium silicon oxynitride, aluminum siliconoxynitride, lanthanum silicon oxynitride, titanium silicon oxynitride,and tantalum silicon oxynitride.
 16. The method of claim 1 wherein afterthe introducing, the concentration proximate the first surface is on theorder of approximately 4×10²¹ per cm³ and wherein the concentrationproximate the second surface is on the order of approximately 2×10²⁰ percm³.
 17. The method of claim 1 wherein the introducing forms a barrierlayer including the diffusion barrier material in an upper portion ofthe first dielectric layer.
 18. The method of claim 1 furthercomprising: forming a layer of gate material over the second dielectriclayer; patterning the layer of gate material to form a gate from thelayer of gate material, the gate located over the second dielectriclayer.